When a fatty acid ester is allowed to react with metallic sodium in benzene, toluene or the like inert solvent, an acyloin (α-hydroxy ketone) is obtained by so-called acyloin condensation. In this case, it is known that a medium to large ring acyloin is formed by intramolecular condensation when a diester of a fatty acid having 5 or more carbon atoms is used, and a method has been proposed for the production of cyclopentadecanone as one of musk aromatic components, by carrying out dehydration and reduction reactions using 2-hydroxycyclopentadecanone as this acyloin (Japanese Patent No. 3087921, JP-A-2002-220361).
Broadly known as this dehydration reduction reaction includes a method in which an acyloin is converted into corresponding ketone by directly reducing it in the presence of zinc and hydrochloric acid, sulfuric acid or the like mineral acid and a two-stage method in which an acyloin is firstly dehydrated to convert it into an α, β-unsaturated ketone which is then hydrogenated to convert it into corresponding ketone. Regarding the former zinc-acid direct reduction method, it is considered that the reaction progresses through the transfer of two electrons from zinc to the carbonyl group of acyloin, subsequent leaving of the α-position hydroxyl group and simultaneous addition of proton of the acid to the formed enolate, so that its reaction mechanism is completely different from the latter two-stage method in which the material is dehydrated and then reduced.
In the aforementioned zinc-acid direct reduction method, chemically equivalent amount of zinc is required and zinc is consumed simultaneously with the reaction, but a side reaction occurs in which zinc is wastefully consumed by simply reacting with the acid, so that it poses a problem in terms of a waste treatment such as recovery of zinc, and since the reduction reaction occurs on the metal surface, it is necessary to highly disperse zinc in the two phases of mineral acid aqueous solution and organic solvent, and for obtaining agitation necessary for the sufficient dispersion, it is necessary to use a reactor having a relatively small volume, so that it also poses a problem when scale up is taken into consideration for the improvement of production efficiency.
In the two-stage method, on the other hand, the dehydration reaction and hydrogenation reaction are carried out as separate steps, and the product is once separated after completion of the dehydration reaction and transferred into another reaction vessel to carry out the hydrogenation reaction, so that the reaction operations are complex and become a cause of increasing the cost.
Reference 1: Japanese Patent No. 3087921
Reference 2: JP-A-2002-220361